The present invention relates to a process for producing silicone compounds and more particularly the present invention relates to a catalyst in the basic process for producing organo silanes, the basic material to make silicone compounds.
The basic process for producing silicones generally comprises reacting an organohalide in the presence of a catalyst with silicon metal to produce organohalosilanes. The organohalide can be for instance methyl chloride, phenyl chloride, vinyl chloride and other organohalides. The silicon metal is preferably present in the form of silicon particles of relatively high purity, that is silicon material comprising at least 95% of silicon.
The catalyst that is preferred in most processes is a partially oxidized copper metal catalyst in the form of a powder. This basic process is disclosed in Rochow U.S. Pat. No. 2,380,995 which is hereby incorporated by reference. By means of this process there is produced a mixture of organohalosilanes which from a methyl chloride reactant the products can be for instance, Me.sub.2 SiCl.sub.2, Me.sub.4 Si, Me.sub.3 SiCl, MeSiCl.sub.3, SiCl.sub.4, HSiCl.sub.3, MeHSiCl.sub.2, Me.sub.2 HSiCl. Although most of these products find some use, the most preferable is dimethyldichlorosilane, Me.sub.2 SiCl.sub.2.
Normally, the process results in a sizable yield of organohalosilanes. Fortunately, most of this yield is in a form of Me.sub.2 SiCl.sub.2, that is dimethyldichlorosilane or broadly, diorganodichlorosilane and also MeSiCl.sub.3 which broadly is organotrichlorosilane. While the organotrihalosilane or methyltrichlorosilane have certain utilities by far it is preferred to maximize the yield of dimethyldichlorosilane. While the monomethyltrichlorosilane has limited uses in the production of silicone resins and in the production of trifunctional fluids, the diorganodichlorosilane (difunctional) silane is most preferred since it can be utilized to produce a variety of silicone products. For instance, it can be utilized as an ingredient in the production of silicone resins. However, by far its most prevalent use is as an intermediate in the production of linear diorganopolysiloxane polymers of wide viscosity range; that is, polymers in the viscosity range 100 to 10,000,000 centipoise and polymers in the viscosity range of 1,000,000 to 300,000,000 centipoise at 25.degree. C.
These higher viscosity polymers are normally referred to as gums and are utilized as the base polymer in the production of heat vulcanizable silicone rubber compositions. The linear low viscosity fluids, when they are for example triorganosiloxy end-stopped, can be utilized as base fluids in the production of various silicone greases and various other types of silicone fluids. It should be noted above and below that while the discussion may be in some cases with respect to methyl, the same comments apply to cases where the organo group in the organohalosilane product of the basic silicon reaction is other than methyl, such as phenyl, vinyl, etc.
One broad use of such diorganodichlorosilanes is in the production of silanol end-stopped diorganopolysiloxane polymers of a viscosity varying from 100-1,000,000 to 10,000,000 centipoise and preferably from 100-1,000,000 centipoise at 25.degree. C. Such silanol terminated polymers are utilized in the production of various types of room temperature vulcanizable silicone rubber compositions, both of the one-component type and the two-component type. An example of such linear triorganosiloxy end-stopped diorganopolysiloxane polymers in heat vulcanizable silicone rubber compositions is, for instance, disclosed in the DeZuba et al, U.S. Pat. No. 3,730,932 which is hereby incorporated by reference. An example of the silanol terminated polymers which are produced again by the further processing of the diorganodihalosilanes such as dimethyldichlorosilane is, for instance, disclosed in Beers U.S. Pat. No. 4,100,129 and Peterson, U.S. Pat. No. 4,250,290 which are hereby incorporated by reference.
These latter two patents disclose the use of the base silanol terminated polymers utilized to produce room-temperature vulcanizable silicone rubber compositions and the process of producing such base silanol polymers from the diorganodihalosilane. The foregoing U.S. Pat. No. 4,100,129 is just an example of one type of room-temperature vulcanizable silicone rubber composition that can be produced from such silanol polymers. There are many types of such compositions.
Basically speaking, the polymers produced can be both of the room temperature vulcanizable and of the heat vulcanizable types. The diorganodihalosilanes are first hydrolyzed with water, and then there is added to the hydrolyzate an alkali metal catalyst and the resulting mixture heated at elevated temperatures (that is, temperatures above 150.degree. C.). Accordingly there is preferentially distilled and collected overhead cyclotetrasiloxanes. These cyclotetrasiloxanes are collected in a relatively pure form and then they are reacted in one particular type of process; either with triorganosiloxy chain stoppers or with water in the presence of an alkali metal hydroxide catalyst at elevated temperatures so as to produce linear polymers. The foregoing exemplary patents have been given above and the method of producing such polymers is well known in the art. Proceeding to the initial reactions, that is, in the production of the diorganodihalosilane, there have been various improvements on the Rochow process as exemplified by the following patents. One of the improvements is that of Dotson U.S. Pat. No. 3,133,109 which discloses the utilization of a jet mill to comminute the silicon particles as utilized in a fluidized bed reactor so as to increase the yield of organohalosilanes from the silicon metal. Another example of increasing the yield of the basic Rochow process is, for instance, the disclosure of R. Shade, U.S. Pat. No. 4,281,149 which discloses the abrading of certain of the silicon particles from the fluidized bed so as to increase overall process silicon utilization. Another example of an improvement is that disclosed in Ritzer et al, patent application Ser. No. 209,635, now U.S. Pat. No. 4,307,242 which is hereby incorporated by reference, which discloses the classification of certain of the particles that are taken out of the fluidized bed of the reactor and recycled for the purpose of increasing the yield of the desired product that is obtained from the silicon particles in the fluidized bed of the reactor. Accordingly, some of the work that has been done as disclosed above is so as to increase the amount of general product that is obtained in terms of the silicon metal that is fed into the reactor.
Further, the reactor can be either a stirred-bed or a fluidized bed reactor. However, it has been found that the maximum yield is obtained from the process by the use of a fluidized bed reactor utilizing gaseous organohalides, silicon metal and copper catalyst as small particles.
In addition, another approach in maximizing the desirable yield from the reaction has been to study the means by which the yield of diorganodihalosilane is maximized from a given quantity of silicon metal and copper catalyst. It is normally desirable to obtain as low a T/D ratio (T being the mono-organotrihalosilane and D being the diorganodihalosilane) as possible. One method of trying to increase such yield of diorganodihalosilane corresponding to the respective yield of mono-organotrihalosilane from the Rochow or direct process, has been the development of an efficient catalyst which maximizes such a yield. Traditionally, there has been utilized a copper catalyst usually modified with a promoter such as zinc. Performance varied markedly with the initial form of the copper. Generally, such copper catalysts were made from cemented copper, produced by the copper cementing process, containing free copper, copper oxides, several impurities such as, for instance, iron, tin, aluminum, lead, etc.
An example of one attempt to improve over such a copper catalyst for the direct Rochow process is, for instance, disclosed in Maas et al. U.S. Pat. No. 4,218,387 which is hereby incorporated by reference. This patent emphasized the production of a copper oxide catalyst for the direct process by the partial oxidation of copper produced by various means such as the cemented copper process. It should be noted that this patent emphasizes that only partial oxidation is to take place in the formation of the catalyst and not complete oxidation and the reference based the beneficial results of the catalyst (or the process by which it is prepared) in terms of utilizing a partially oxygenated atmosphere for the oxidation; i.e., gas with an oxygen partial pressure less than that of air and the absence of a reducing atmosphere in the oxidation gasses utilized to produce the copper catalyst of Maas et al. However, while this catalyst, was an improved catalyst it still was not as effective as would be desired. Further, the process of the preparation of this catalyst did not pay sufficient attention to the physical characteristics of the copper catalyst particles. In addition, there was the presence of certain oxides as well as copper metal in certain concentrations in the copper catalyst. Accordingly, it was highly desirable to produce a copper catalyst for utilization in the direct process which was an improvement over that of the prior art as well as that of the Maas et al patent which would result in improved yields of diorganodihalosilanes.